In a hard disk drive of this type the magnetic disk or the disk pack, the carrier arrangement for the magnetic heads and if necessary the disk driving mechanism are completely encased in order to prevent the penetration of contaminations into the disk drive. This means that the user of the disk drive cannot remove the magnetic disks. In the case of repairs on the hard disk drive, the latter must be shipped as a whole to the manufacturer or the repair service, in which case the magnetic disks must necessarily be handed over to the manufacturer or the repair service. Since the most frequent defects in disk drives concern precisely the electronic components, the user in this case often no longer has the capability of affecting the information stored on the disks by the use of magnetic heads in the normal way. However, here the possibility exists under some circumstances that during or after the repair of the disk drive unauthorized persons may be able to read information stored on the disks.
For this reason, the invention is based on the problem of ensuring, for a hard disk drive of the type mentioned at the start, that even in the case of a failure of the disk drive the capability still exists of preventing unauthorized persons from having access to the information stored on the magnetic disk.
This problem is solved according to the invention by having at least one permanent-magnet or electromagnetic erase head arranged in the housing which head can operate independently of the magnetic heads. According to a first embodiment example the erase head is arranged on an erase arm which is movable relative to the magnetic disk. Theoretically, an electromagnetic erase head could also remain in a stationary position relative to the magnetic disk, since it becomes active only through being energized with current. Since however, the airflow conditions in the disk region are disturbed by the erase head and the erase arm, it is expedient for the erase head to be able to be removed from the disk region in normal operation. It is advantageous for the erase arm to be pivotable on the housing around a pivoting axis aligned parallel to the magnetic disk axis. For this, the erase arm may be movable manually or by motor.
In a disk drive with a disk pack including a plurality of disks, the erase heads can be swung in between the magnetic disks, one erase head being provided per disk surface. For a plurality of magnetic disks, the arrangement may also be made such that only part of the disk surface is assigned to one particular erase head. This offers the capability, for example, of storing sevice information on one or two disk surfaces of the pack which is required for a test run of the disk drive and hence is not to be erased. However, the arrangement can also be made such that the erase head in its erase position extends over only a part of the magnetic disk surface, so that the service information mentioned can be stored on the region of the disk not covered by the erase head.
When an air conduction comb is assigned to the disk pack, as will be described in detail below on the basis of FIG. 2, then according to a second embodiment example the erase heads may also be arranged on fingers or teeth of the air conduction comb engaging between the magnetic disks.
According to a third embodiment example, finally, the erase heads can also be arranged directly on the carrier arms for the read/write heads and next to the latter. This has the advantage that the erase heads require no carrier arrangement of their own when this carrier is not present as such, for example, if it is present in the form of the air conduction comb.
In order to make erasing possible even in the case of a failure of the magnetic disk drive, it may be provided that the magnetic disk is rotatable manually by at least 360.degree.. This can be done with the use of a key or a tool.
In order to prevent any unintentional erasing of the information stored on the disks, it is expedient for the erase arm to be lockable in its rest position. For an electromagnetic erase head, the switching-on mechanism for the erase head may be lockable. The locking here may be done with a lock, so that only the possessor of the key can erase the information with the aid of an additional erase unit and thus he retains control over the erase process. In order to prevent any malfunction of the disk drive, the locking of the erase heads may be coupled with the regulating device for the magnetic heads in such a way that unlocking is possible only in the rest position of the magnetic heads.
Besides the capability of making the stored information unreadable without the use of an operative read/write unit and thus deny access to unauthorized persons, the solution according to the invention also offers another advantege. When a disk drive must be taken apart because of a defect, it need not necessarily be returned to the user. It is immediately replaced by a serviceable disk drive. The service organization need not be concerned about the stored information and if necessary can install the repaired disk drive without difficulty for another user. Formerly this would have been possible only if the service organization after repairing the defective disk drive had made the stored information unusable through time-consuming overwriting.
Further features and advantages are seen from the following description, which in connection with the annexed drawings will explain the invention on the basis of embodiment examples. In these: